Hydraulic Servo Systems Analysis And Design

This book has been written for those who design and use hydraulic systems and, indeed, for any reader who is interested in this comparatively little known subject. It is based on reports and notes which I have compiled but not previously published in the course of many years' work on aircraft hydraulic systems. It is not a theoretical treatise which claims to clarify or re-examine any particular field of fluid mechanics, nor is it a technological catalogue with detailed descriptions and limited scope. It contains the general laws and methods of analysis which are already known but not as yet set down in any one textbook. These laws and methods are illustrated by numerous examples, taken from actual industrial problems, with numerical data corresponding to modern hydraulic equipment. The material is presented in such a way as to make it useful to the practical engineer.

The analysis of hydraulic circuits is supposedly difficult because of the non-linearity of the associated equations. It is rare, however, that these equations cannot be easily and validly linearized in the neighbourhood of an operating point. It is therefore natural to divide this book into two main parts, corresponding to the two successive stages in the analysis of a hydraulic system.

The first part, called 'Static Performance', deals with the determination of steady-state conditions.

The second part, called 'Dynamic Performance', deals with the transient behavior of the system about the steady-state condition, i.e. essentially problems of stability, response speed and accuracy.

There is a third part which contains suitable examples illustrating the application of the methods of analysis derived in the first two parts.

The problems encountered in hydraulics can generally be divided into a limited number of groups, regardless of the type of equipment involved, and these groups are dealt with in separate Chapters. This method of presentation has its disadvantages. The more experienced reader may be annoyed to find certain apparently obvious points dealt with in too much detail. These seemingly superfluous Sections, however, have been included at the request of engineers who were kind enough to read the original manuscript and even to put it to the test as a handbook in everyday use. For this reason, a number of diagrams and equations have been repeated in the practical examples, in order to save time and to avoid possible mistakes. There is also a certain degree of elaboration on general points such as the concept of loss of head, a section on forces and stiffness, etc. which the reader may consider as out of place, but which provide an opportunity of revising the basic concepts involved in the later analyses.